Downwind drift and deposition of malathion on human targets from ground ultra-low volume mosquito sprays

Malathion was sprayed using a truck-mounted ultra-low volume (ULV) aerosol generator. The generator was operated at 41.4 kPa (6 psi) at flow rate of 128 ml (4.3 fl. oz.) per min. Malathion concentrations were measured at selected positions on live, stationary human subjects wearing protective clothing and placed along a transect at right angles to the path of the truck. Two standing subjects were exposed downwind to the malathion spray at 7.6 and 15.2 m. A third subject was exposed while jogging in the same direction as the spray vehicle and 1.5 m from the spray path. No significant differences (P > 0.05) in total amount of malathion deposited on subjects was demonstrated. During the last 4 sprays, average amounts of malathion deposited on ground level at 15.2, 30.4 and 91.2 m were not significantly different (P > 0.05). Malathion dermal residues were compared with the acute LD50 value (4,100 mg/kg) for a 70 kg adult male. Calculated malathion dermal exposures were less than the acute lethal dose for a human subject by 4 orders-of-magnitude or more.